Published methods for the isolation of rat brain synaptosomes will be modified to yield a preparation with suitably intact plasma membranes and lack of mitochondrial contamination to study the distribution of hexokinase between mitochondrially bound and soluble forms as a function of energy supply and demand. These studies when completed will be extended to other relevant enzymes, e.g. phosphofructokinase, aldolase, lactic dehydrogenase and creatine kinase.